Multicore cable

Abstract

This multicore cable has: two insulated wires each having a conductor and an insulating layer; and a sheath that collectively covers the two insulated wires. The insulating layer is formed from an ethylene-vinyl acetate copolymer resin. The sheath is formed from an ethylene-ethyl acrylate copolymer resin, and the pulling force of the insulated wires from the sheath is between 5 N / 30 mm and 35 N / 30 mm, inclusive.

Description

Multi-core cable

[0001] The present disclosure relates to multi-conductor cables.

[0002] Patent Document 1 discloses a method for manufacturing a multi-core cable with a resin molded body, in which molten resin is supplied to the connection portion between the lead wires and the electric wires.

[0003] Japanese Patent Application Publication No. 2017-007307

[0004] A multi-core cable according to one embodiment of the present disclosure comprises: two insulated wires each having a conductor and an insulating layer; and a sheath that collectively covers the two insulated wires, wherein the insulating layer is formed of an ethylene-vinyl acetate copolymer resin; the sheath is formed of an ethylene-ethyl acrylate copolymer resin; and the pull-out force of the insulated wires from the sheath is 5 N / 30 mm or more and 35 N / 30 mm or less.

[0005] Fig. 1 is a schematic cross-sectional view showing an example of a multi-core cable according to the present disclosure. Fig. 2 is a schematic diagram showing a pull-out test method. Fig. 3 is a schematic diagram showing a flame retardancy test method. Fig. 4 is a schematic diagram showing a waterproofing test method.

[0006] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide a multi-core cable with improved terminal processability.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a multi-core cable with improved terminal processability.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. A multicore cable according to one aspect of the present disclosure includes: (1) two insulated wires each having a conductor and an insulating layer, and a sheath that collectively covers the two insulated wires, wherein the insulating layer is formed of an ethylene-vinyl acetate copolymer resin, the sheath is formed of an ethylene-ethyl acrylate copolymer resin, and the pull-out force of the insulated wires from the sheath is 5 N / 30 mm or more and 35 N / 30 mm or less.

[0009] According to this configuration, the sheath can be easily removed at the tip of the multi-core cable to expose the insulated wires, thereby providing a multi-core cable that is easy to process at the end.

[0010] (2) In the above (1), the multi-core cable may have flame retardancy that passes the VW-1 vertical flame test of the UL224 standard.

[0011] According to this configuration, the cable has flame retardancy that can pass the VW-1 vertical flame retardancy test, and therefore, it is possible to provide a multi-core cable suitable for applications that require flame retardancy.

[0012] (3) In the above (1) or (2), a flame retardant may be added to the sheath and the insulating layer, and the thickness of the sheath may be greater than the thickness of the insulating layer.

[0013] According to this configuration, a flame retardant is added to both the sheath and the insulating layer, and the thickness of the sheath is greater than the thickness of the insulating layer, thereby providing a multi-core cable with improved flame retardancy.

[0014] (4) In any one of (1) to (3) above, the thickness of the insulating layer may be 0.2 mm or more and 0.5 mm or less.

[0015] This configuration makes it possible to provide a multi-core cable suitable for applications requiring flexibility.

[0016] (5) In any one of (1) to (4) above, the thickness of the sheath may be 0.4 mm or more.

[0017] This configuration makes it possible to provide a multi-core cable suitable for applications requiring flame retardancy.

[0018] (6) In any one of (1) to (5) above, the multi-core cable has flame retardancy that passes the VW-1 vertical flame test of the UL758 standard, the sheath and the insulating layer each contain a flame retardant, the thickness of the sheath is thicker than the thickness of the insulating layer, the thickness of the insulating layer is 0.2 mm or more and 0.5 mm or less, and the thickness of the sheath may be 0.4 mm or more.

[0019] This configuration makes it possible to provide a multi-core cable suitable for applications requiring flame retardancy and flexibility.

[0020] [Details of the embodiments of the present disclosure] Specific examples of multi-core cables according to the embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0021] A multi-core cable 1 according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing an example of a multi-core cable 1 according to the present disclosure. The multi-core cable 1 according to this embodiment can be used, for example, for wiring a thermocouple. As shown in Fig. 1, the multi-core cable 1 has two insulated wires 10 and a sheath 2 that collectively covers the two insulated wires 10.

[0022] The insulated wire 10 includes a conductor 10a and an insulating layer 10b. The conductor 10a is a single wire made of a conductive metal such as a copper alloy, or a twisted wire made by twisting together multiple thin wires. The insulating layer 10b is made of ethylene-vinyl acetate copolymer (EVA) resin and protects the conductor 10a while electrically insulating it from its surroundings. In the multi-core cable 1 according to the present disclosure, two insulated wires 10 are formed by simultaneously extruding the insulating layer 10b around the two conductors 10a. When extruding the insulating layer 10b, the insulating layer 10b is also extruded between the two insulated wires 10, forming a joint 11. In other words, the two insulated wires 10 are joined together by the joint 11. The insulating layer 10b may be thin to improve the flexibility of the multi-core cable 1 according to the present disclosure. Therefore, the insulating layer 10b may be 0.2 mm or more and 0.5 mm or less in thickness. The insulated wire 10 used in the present disclosure is not limited to the above embodiment, and for example, the two insulated wires 10 may be formed by extrusion molding separately.

[0023] The sheath 2 is formed of ethylene-ethyl acrylate copolymer resin (EEA) and covers the two insulated wires 10. In the multi-core cable 1 according to the present disclosure, the sheath 2 is formed by draw-down extrusion molding, and a partial gap is generated between the insulated wires 10 and the sheath 2. From the viewpoint of improving the flame retardancy of the multi-core cable 1, the thickness of the sheath 2 may be 0.4 mm or more.

[0024] In the multi-core cable 1 according to the present disclosure, the pull-out force of the sheath 2 against the insulating layer 10b is 5 N / 30 mm or more and 35 N / 30 mm or less. If the pull-out force is 35 N / 30 mm or more, it becomes difficult to pull out and remove the sheath 2 alone, resulting in a decrease in the terminal workability of the multi-core cable 1. If the pull-out force is 5 N / 30 mm or less, the insulated wire 10 may become misaligned with respect to the sheath 2. By setting the pull-out force of the sheath 2 against the insulating layer 10b to 5 N / 30 mm or more and 35 N / 30 mm or less, it becomes easier to remove the sheath 2 alone while maintaining adhesion between the sheath 2 and the insulated wire 10, thereby improving the terminal workability of the multi-core cable 1. The pull-out force can be adjusted, for example, by adjusting the pull-down extrusion conditions of the sheath 2.

[0025] A flame retardant is added to the insulating layer 10b and the sheath 2 to improve flame retardancy. The flame retardant added to the insulating layer 10b and the sheath 2 may be a bromine-based flame retardant, antimony trioxide, zinc borate, metal oxide, metal hydroxide, or the like. In this embodiment, a bromine-based flame retardant, antimony trioxide, and zinc borate are added to the insulating layer 10b and the sheath 2. The flame retardants added to the insulating layer 10b and the sheath 2 may be the same or partially different.

[0026] In the multi-core cable 1 according to the present disclosure, different resins are used for the sheath 2 and the insulating layer 10b. This prevents the sheath 2 and the insulating layer 10b from being strongly adhered to each other, improving terminal processability. Furthermore, in the multi-core cable 1 according to the present disclosure, the sheath 2 is manufactured by draw-down molding. This reduces excessive adhesion between the sheath 2 and the insulated wire 10, improving terminal processability.

[0027] In the multi-core cable 1 according to the present disclosure, the insulating layer is formed from EVA. EVA has high adhesion to epoxy resin, which is generally used as a molding resin, and is highly watertight. Therefore, the multi-core cable 1 according to the present disclosure is particularly useful in an environment where the sheath 2 is removed at the terminal to expose the insulated wires 10 and then molded with epoxy resin.

[0028] Examples Next, examples of the present disclosure will be described. Multi-core cables according to the following Examples 1 to 4 were prepared, and pull-out tests and flame retardancy tests were conducted on the multi-core cables to measure their terminal workability and flame retardancy. In addition, assuming a case in which the insulated wires of the multi-core cables are used in a state where they are molded with epoxy resin, a waterproofing test was conducted on the insulated wires.

[0029] The multi-core cable of Example 1 had the same configuration as the multi-core cable 1 described in the above embodiment, and was set as follows. Seven tin-plated annealed copper wires with a diameter of 0.16 mm were twisted together to form two conductors with an outer diameter of 0.48 mm. The two conductors were covered with EVA by extrusion molding to a thickness of 0.3 mm to form a joint, resulting in two insulated wires with a cross-section shaped like glasses. The outer diameter of each insulated wire was 1.08 mm. These insulated wires were covered with EVA by drawing molding to a thickness of 0.5 mm to form a sheath. Example 2 was manufactured under the same conditions as those described above, except for the sheath thickness, and formed so that the sheath thickness was 0.3 mm.

[0030] Two types of multi-core cables were produced for comparison with Examples 1 and 2. The multi-core cable of Example 3 differs from the multi-core cable of Example 1 in that EVA is used for the sheath. The multi-core cable of Example 4 is the same as Example 1 in that different resins are used for the insulating layer and the sheath, but differs from the multi-core cable of Example 1 in that EEA is used for the insulating layer and EVA is used for the sheath. Note that Examples 3 and 4 had the same configuration as Example 1 except for the above-mentioned differences from Example 1.

[0031] The differences in the configuration of the multi-core cables of Examples 1 to 4 are shown in Table 1.

[0032]

[0033] (Pull-out test) A pull-out test was performed on the multi-core cables of Examples 1 to 4. FIG. 2 is a schematic diagram showing the pull-out test method. The pull-out test is performed by pulling out a portion of the sheath 2 of the multi-core cable 1 using a pull-out tester 100. The pull-out tester 100 has a pinch part 101 that grips the tip of the multi-core cable 1 and a holding part 102 that grips a portion of the multi-core cable 1 away from the end. During the pull-out test, an incision K is made in the sheath 2 of the multi-core cable 1 to divide the sheath 2 into a removed portion 2a and a non-removed portion 2b. The distance L from the incision K to the end of the removed portion 2a is 150 mm. During the pull-out test, the pull-out tester 100 holds down the non-removed portion 2b with the holding portion 102, then clamps the removed portion 2a with the pinching portion 101 and pulls out the removed portion 2a parallel to the axis of the multi-core cable 1 (in the direction indicated by the arrow in Figure 2).

[0034] In the pull-out test, the pulling speed was set to 200 mm / sec, and the maximum tensile load when 30 mm of the sheath was completely removed was measured. The pass / fail result of the pull-out test was determined to be a pass if the maximum tensile load was 5 N or more and 35 N or less. As a result of the pull-out test, the multi-core cables of Examples 1, 2, and 4 passed, but the multi-core cable of Example 3 failed.

[0035] (Flame Retardance Test) A flame retardance test was conducted on the multi-core cables of Examples 1 to 4. The flame retardance test was conducted in accordance with the vertical flame test (VW-1) in the UL758 standard. Figure 3 is a schematic diagram showing the flame retardance test method. In the flame retardance test, kraft paper 51 is placed on top of a vertically arranged multi-core cable 1. Surgical cotton 52 is placed on the bottom of the multi-core cable 1.

[0036] In the flame retardancy test, five cycles were performed, each cycle consisting of ignition of the burner 50 for 15 seconds and a rest of 15 seconds, and the pass / fail of the flame retardancy test was judged based on the degree of combustion of the multi-core cable 1, the kraft paper 51, and the surgical cotton 52. At the end of the test, if a flame remained on the multi-core cable 1 for more than 60 seconds, if more than 25% of the kraft paper 51 was burned, or if the surgical cotton 52 was burned, the test was deemed to have failed, and all other cases were deemed to have passed. As a result of the flame retardancy test, the multi-core cables of Examples 1 and 4 passed, while the multi-core cables of Examples 2 and 3 failed.

[0037] (Waterproofing Test) A waterproofing test was conducted on the multi-core cables of Examples 1 to 4. Fig. 4 is a schematic diagram showing the waterproofing test method. The waterproofing test was conducted on a circuit unit 200 in which the sheath 2 and the insulating layer 10b of the insulated wire 10 were stripped in stages at the end of the multi-core cable 1 to expose the conductor 10a, and the conductor 10a was then electrically connected to a circuit board 201 by soldering. As shown in Fig. 4, in the circuit unit 200, the conductor 10a and the insulating layer 10b were molded on the circuit board 201 with epoxy resin M.

[0038] In the waterproofing test, the insulation resistance value of the circuit unit 200 was measured, and then the circuit unit 200 was completely immersed in water and the insulation resistance value was measured again. The waterproofing test was judged to have passed if the insulation resistance value of the circuit unit 200 after immersion in water had a change rate of within ±2% from before immersion in water. As a result of the waterproofing test, the multi-core cables of Examples 1, 2, and 3 passed, but the multi-core cable of Example 4 failed.

[0039] The test results of the pull-out test, flame retardancy test, and waterproofing test are summarized in Table 2. In Table 2, the results of each test are indicated as A for pass and B for fail.

[0040]

[0041] The multi-core cable of Example 3 failed the pull-out test and the flame retardancy test. The multi-core cable of Example 3 used EVA for both the insulation layer and the sheath, and it is believed that the strong adhesion between the insulation layer and the sheath reduced the pull-out resistance. The multi-core cable of Example 4 failed the waterproofing test. It is believed that this is because the EEA used in the insulation layer of the multi-core cable of Example 4 has poorer adhesion to the epoxy resin than EVA.

[0042] The multi-core cable of Example 2 passed the pull-out test and the waterproof test. This is thought to be due to the fact that the resin composition of the insulation layer and the sheath was different, and EVA, which has high adhesion to epoxy resin, was used for the insulation layer. Furthermore, Example 1 passed the flame retardancy test in addition to the pull-out test and the waterproof test. This is thought to be due to the fact that, in addition to the above-mentioned configuration, the sheath was made thicker than the insulation layer, thereby improving flame retardancy.

[0043] Although the embodiments of the present disclosure have been described above, it goes without saying that the technical scope of the present disclosure should not be interpreted as being limited by the description of the present embodiments. The present embodiments are merely examples, and it will be understood by those skilled in the art that various modifications of the embodiments are possible within the scope of the invention described in the claims. The technical scope of the present disclosure should be determined based on the scope of the invention described in the claims and its equivalents.

[0044] This application claims priority based on Japanese Application No. 2023-144206 filed on September 6, 2023, and incorporates by reference all of the contents of the aforementioned Japanese application.

[0045] REFERENCE SIGNS LIST 1 multi-core cable 2 sheath 2a removed portion 2b non-removed portion 10 insulated wire 10a conductor 10b insulating layer 11 joint portion 50 burner 51 kraft paper 52 surgical cotton 100 pull-out tester 101 pinch portion 102 holding portion 200 circuit unit 201 circuit board

Claims

1. A multi-core cable comprising: two insulated wires each having a conductor and an insulating layer; and a sheath covering the two insulated wires together; the insulating layer is formed from an ethylene-vinyl acetate copolymer resin; the sheath is formed from an ethylene-ethyl acrylate copolymer resin; and the pull-out force of the insulated wires from the sheath is 5 N / 30 mm or more and 35 N / 30 mm or less.

2. The multi-core cable according to claim 1, wherein the multi-core cable has flame retardancy that passes the VW-1 vertical flame test of the UL758 standard.

3. A multi-core cable as claimed in claim 1 or 2, wherein a flame retardant is added to the sheath and the insulating layer, and the thickness of the sheath is greater than the thickness of the insulating layer.

4. A multi-core cable as claimed in any one of claims 1 to 3, wherein the thickness of the insulating layer is between 0.2 mm and 0.5 mm.

5. A multi-core cable as claimed in any one of claims 1 to 4, wherein the thickness of the sheath is 0.4 mm or more.

6. The multi-core cable according to claim 1, wherein the multi-core cable has flame retardancy that passes the VW-1 vertical flame test of the UL758 standard, a flame retardant is added to each of the sheath and the insulating layer, the thickness of the sheath is thicker than the thickness of the insulating layer, the thickness of the insulating layer is 0.2 mm or more and 0.5 mm or less, and the thickness of the sheath is 0.4 mm or more.

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